In the related art, a refrigerating and air-conditioning apparatus has a refrigeration cycle including a compressor, a condenser, expansion means, and an evaporator, and the refrigeration cycle is filled with a refrigerant. The refrigerant compressed by the compressor becomes a high-temperature high-pressure gas refrigerant and is sent to the condenser. The refrigerant flowing into the condenser is liquefied by releasing heat to the air. The liquefied refrigerant is decompressed to a two-phase gas-liquid state by the expansion means, and is gasified in the evaporator by absorbing heat from ambient air. The gasified refrigerant then returns to the compressor.
A refrigerated warehouse needs to be controlled such that the temperature range therein is lower than 10° C. Because the evaporating temperature of the refrigerant in this case is lower than 0° C., frost is formed on the surfaces of fins of the evaporator as time elapses. When frost is formed, the cooling capacity is lowered due to reduced airflow and increased thermal resistance, thus requiring regular defrosting operations for removing the frost.
When the defrosting operation is performed, the frost adhered to the surface of the evaporator melts and drips down. Therefore, a drain pan for receiving the so-called drain-water, that is, the dripping water, is disposed in the refrigerating and air-conditioning apparatus. The drain-water dropping onto the drain pan is drained from a drain outlet provided in the drain pan. In a case where the outside temperature is low, for example, the drain-water may freeze, making it difficult to drain the drain-water. Hence, the drain-water is prevented from freezing by attaching a heater to the drain pan.
Defrosting the evaporator and heating the drain pan more than necessary may lead to waste of power consumption as well as temperature increase in the refrigerated warehouse. Therefore, it is necessary to accurately determine the frosting condition so as to appropriately perform the defrosting and the heating at optimal timings. In the related art, there is a refrigerating apparatus in which a heat transfer member is provided in contact with both the evaporator and the drain pan, and a temperature sensor is attached to this heat transfer member. The temperature of the heat transfer member detected by the temperature sensor is detected as the temperature of both the evaporator and the drain pan. By determining the frosting condition from the detected temperature, control is performed to defrost the evaporator and to turn the drain-pan heater on and off (for example, see Patent Literature 1).
Furthermore, in the related art, there is also a refrigerating apparatus that starts defrosting operation in accordance with a predetermined defrosting cycle regardless of the frosting condition.